The basic concept of run flat tires has been around for many years. Many of the early inventions, such as U.S. Pat. No. 4,130,154 (1978) used separate support members that were applied to the wheel rim. These support members provided a secondary device to support the tire in an uninflated condition. Advancements in rubber compounding technology, as well as tire building techniques, have made it possible to incorporate the uninflated support capabilities into the tire sidewall itself. This provides for a more practical solution to the run flat engineering problem due to a reduction in complexity. One of the early patents that utilized this approach was U.S. Pat. No. 4,193,437 (1980). This concept used an insert of rubber material in the tire sidewall that provided the necessary extra support to allow the tire to run without inflation. Many patents have since been issued to various companies that are all modifications of this same basic approach. Some examples include U.S. Patents:
U.S. Pat. No. 4,405,007 (1983) U.S. Pat. No. 5,368,082 (1994), and U.S. Pat. No. 5,639,320 (1997) to Goodyear, PA1 U.S. Pat. No. 5,427,166 (1995), U.S. Pat. No. 5,511,599 (1996), and U.S. Pat. No. 5,868,190 (1999) to Michelin, PA1 U.S. Pat. No. 4,779,658 (1988), U.S. Pat. No. 4,917,164 (1990), U.S. Pat. No. 5,217,549 (1993), U.S. Pat. No. 5,427,176 (1995), and U.S. Pat. No. 5,529,105 (1996) to Firestone.
These patents generally use different construction and compound techniques to reach the goal of good run flat performance. However, one feature they all have in common is that they use sidewall inserts that essentially extend substantially the full radial sidewall length. This approach places a very difficult set of engineering requirements on one piece of material. Such material must provide adequate support and heat resistance performance for the entire sidewall height. Different zones in the sidewall have different performance characteristics. The upper sidewall region for instance is subjected to high flex and heat resistance requirements in the uninflated state. The lower sidewall zone, however, is subjected to much less stress. Moreover, the use of inserts that extend the full width of the sidewall makes it very difficult to balance tire performance characteristics.
A different concept is used in U.S. Pat. No. 5,309,970 (1994) which utilizes 3 specific sidewall zones. A relatively wide first reinforcing rubber insert transitions to a narrower second reinforcing insert which then transitions to the bead filler.
The characteristics of the above concepts are different from the proposed invention. Such concepts use the softest rubber compound in the upper sidewall region. The next hardest compound is the second reinforcing insert with the bead filler being the hardest compound. This approach has concentrated the stress on the upper first reinforcing insert instead of distributing it throughout the sidewall.
Another concept is set forth in U.S. Pat. No. 5,439,041 (1995) wherein the sidewall contains 3 basic zones. The upper zone in this case does not have any reinforcing insert. The middle section of the sidewall is reinforced with a "elastomeric sponge" type insert with the lower third consisting of a sandwich of this sponge and the bead filler. This concept also concentrates stresses in the upper sidewall region of the tire.
A final concept is set forth in U.S. Pat. No. 5,526,862 (1996) wherein reinforcement does not extend the full length of the sidewall. The inserts are graduated in hardness laterally across the sidewall cross section. The hardest insert is placed in the inner portion of the tire sidewall and makes up a small percentage of the total sidewall height. It is designed for the tire to collapse around this insert in the uninflated state. This concentrates stress in the mid sidewall region of the tire.